The construction of large reactor and transformer cores has been a time and labor intensive task due to the clamp fixturing, lamination alignment, temporary assembly, clamp welding and final assembly which has been required in the assembly process when assembling larger transformers in the 100 KVA to 5,000 KVA power range. The weight of the cores of these transformers ranges from 1000 pounds to more than 15,000 pounds and therefore requires an extremely strong clamp. The core laminations are supported and held in position by clamps, one on each side of the core. It has been the practice to make the clamp from sections of structural steel channel or a combination of structural steel channels and structural steel angles. Structural channels and angles are commercially available in standard sizes. The sizes of structural channels and angles selected for making the clamps are generally those with dimensions closest to the width of the core laminations. Therefore, the clamps provide little if any protection to the edges of the core laminations. The core assembly process starts by fixturing each channel section of the first clamp in proper position with respect to the other channel or angle sections of the clamp. The fixturing must be strong enough to maintain the respective positions of each channel or angle section of the clamp during the laying up of the core laminations. The flanges of channel sections are placed down in the fixture such that the core laminations can be laid on the flat surface of the clamp. Angle sections can be positioned such that flanges are either up or down. When channel and angles are used together, tie straps, which provide a means for alignment and attachment, are welded to each end of the channels. This is done as a subassembly process before core assembly is started. Alignment pins are placed in holes provided in the channels or angles for threaded fasteners used during final assembly of the core. The alignment pins are smooth and slightly smaller in diameter than the threaded fasteners used for final assembly. Each of the many lamination layers of the core consist of thin (5-15 mills thick) segments of magnetizable metal, each individually slidably placed on the alignment pins. Each lamination segment has mitered ends which must be positioned with respect to the adjacent mitered end of the other lamination segments of that layer and with respect to the position of the mitered ends of the previously laid lamination layer segments. After the final core laminations are placed on the stack, the channel and angle sections making up the second clamp are positioned on top of the core stack. A final alignment of the core laminations and clamps is completed and the core assembly is temporarily secured by strapping or banding placed around each leg of the core. Lifting eyes are attached to the clamps and the core assembly is lifted to the upright position. The alignment pins are removed and threaded fasteners installed and tightened. The core assembly is then moved to a welding station where the channel and/or angle sections forming each of the first and second clamps are welded together. After welding, the core assembly is moved to a final assembly area where the coil and various electrical connectors and brackets are installed. Assembling a reactor or transformer core by this method is extremely time consuming and labor intensive. Therefore, it would be desirable to eliminate many of these steps to reduce time and labor cost.